Compatible Systems 5.4 - Manual (Page 283)

Appendices 277
Appendices
IP 101
v Note: This is a very brief introduction to IP networking. For more in-depth
information, there are a number of excellent references. In particular,
Douglas Comer’s Internetworking with TCP/IP (Prentice Hall) is one of the
standard references and provides a wealth of information on the subject.
IP Addresses
Each device on an IP network requires 3 different pieces of information in
order to correctly communicate with other devices on the network: an IP
address, a subnet mask, and a broadcast address. You will usually see each of
these numbers written as four “octets” (e.g. 198.41.12.151, 255.255.255.0,
and 198.41.12.255).
Every IP address is really made up of two pieces: a “network” portion, which
tells routers what group of devices a packet should go to (e.g., any, a campus,
etc.) and a “host” portion which tells routers what specific device among that
group the packet should go to.
By examining the destination address in an IP packet that must be forwarded,
and by using information that has either been statically configured or dynam-
ically gathered from other routers, any router can determine the optimal path
for forwarding packets from one group to another.
Each group of devices on an IP internet needs to have a unique network
portion, and each device within that group also needs a unique host portion.
In the case of the Internet, this uniqueness is made possible by indirectly
getting all network portion assignments through a central clearinghouse
called the Network Information Center or “NIC.” The NIC assigns blocks of
addresses to Internet Service Providers (ISPs), who then assign these
addresses to their customers.
If your network is, or will be, connected to the Internet, you will need to get
a unique network address from your ISP or network administrator.
How much of any given address is the network part and how much is the host
part is determined by the “class” of the network. In each case, the part of the
address not used for the network portion is left as the host portion.